Glass containers of the conventional type for packaging pressurized products like beer and carbonated beverages, will, upon fracture, propel fragments of the glass surrounding the "head space" region of the bottle with the greatest force and velocity. The "head space" is the volumetric portion of the bottle, in upright position, adjacent the shoulder and the neck portions of the glass wall of the glass bottle, and contains compressed gas escaping as carbonation from the beer or beverage product. The head space exists above the fluid level in the bottle and below the cap or closure on the bottle, and is surrounded by the glass wall in the neck portion. It has been found that fractures, fissures or cracks occurring in the glass wall away from the head space region will migrate in the glass wall to the neck and shoulder region at the head space, and with the significantly high pressures of the compressed gas being present, the rupture and fragmentation of the glass wall thereat is most prevalent and severe.
According to the present invention, it is one of the important objects to provide an exterior wrap, such as taught by the U.S. Pat. Nos. 3,760,968; 3,738,524 and 3,604,584, in which the plastic covering is purposely of a variable strength and assembled on the bottle so that the thicker or stronger section of the plastic wrap is matched to overlie the neck section or neck and shoulder sections of the glass wall and encircle the head space.
Another object of the invention is to provide such an overwrap of a foam thermoplastic material to obtain better cushioning and diminish breakage in the container, and, accordingly, achieve a safer pressure glass container.
A further object of the invention is to utilize organic polymeric materials that are economical to manufacture as the overwrap therefrom, and yet are readily and easily printed for label or decorative purposes and provide suitable properties in service for achieving the objectives alluded to herein.
In summary, the principal feature of the invention is to purposely vary the strength, or in most cases the thickness of the plastic wrap or functional coating on a glass bottle whereby the strongest portion of the overwrap on the bottle surface is characteristically along the upper part of the bottle and encircling the head space in the filled container. In the art, the term head space is the volume at the top of the bottle in upright position occurring above the liquid product (beer or beverage) and below the cap on the bottle. The head space contains the highest pressure concentration of gases in the bottle and, if fracture of the glass occurs, propels the fragments with the major force. The purpose of the invention is to improve overall safety of the bottle in use and do so at a practical cost. Data accumulated in practice indicates that breakage of the glass wall almost always includes fracture and fragmentation of the glass in the mentioned head space region.
The present invention is directed to upgrading the overall safety and retention of glass fragments propelled from the bottle should it break in service.
Other objects of the invention are to provide practical and economical methods of producing the overwrap of variable thickness along the axial extent on the bottle wall, as hereinafter are more specifically disclosed.
Several further objects and advantages of the invention will become apparent to those skilled in the art from the descriptions.